A fire detector provided with a differential diaphragm contact means and a contact means which operates at a predetermined temperature in combination is known. For instance, Japanese Utility Model Publication No. 57-27110 (1982) discloses a combination heat-sensing fire detector provided with a differential diaphragm contact means and a contact means which operates by the function of a bimetal member in combination.
This fire detector comprises an air chamber composed of cup-shaped heat-sensing plate, a diaphragm support frame covering the opening of the cup-shaped heat-sensing plate and a diaphragm which is secured to the central opening of the diaphragm support frame. The diaphragm support frame is provided with a vent or leak hole which is a pinhole or a small opening packed with a porous material. An electric contact point is provided at the center of the diaphragm so that the contact point is closed when the diaphragm is deformed and displaced outward. In the center of the bottom of the cup-shaped heat-sensing plate are provided a bimetal member which changes from concave to convex when the ambient temperature reaches a predetermined value and a pin which projects toward the center of the diaphragm supported by a pin guide so that, when the bimetal changes convex, the pin pushes the diaphragm outward causing the electric contact to close.
The thus constructed fire detector operates as follows. When the ambient temperature rapidly rises, the air in the air chamber expands, heated by the heat received by the heat-sensing plate. But the leak hole does not allow rapid leakage of the expanded air, and the diaphragm is deformed so as to close the electric contact. In contrast, when the ambient air temperature rises slowly, the expanded air in the air chamber is allowed to gradually leak out through the leak hole, and therefore the diaphragm does not close the electric contact point. However, when the bimetal member is heated, even slowly, to a predetermined temperature, it turns convex and pushes the pin so as to close the electric contact point. Thus the fire detector is able to generate a fire alarm both when the ambient temperature rises slowly and when it rises rapidly.
However, the operation of the bimetal contact is not so accurate and the degree of the deformation thereof is relatively small and therefore precise design and adjustment are required in this conventional combination heat-sensing fire detector.